This invention concerns improvements in and relating to speech direction-detecting circuits for telephone communication devices. In a variety of telephone devices, it is desirable to provide amplification of speech signals in both directions of transmission. Such devices include, for example, loudspeaking telephone terminals, two wire line repeaters or line extenders, and conference devices incorporating conference bridges and/or conference port repeaters. In such devices it is common practice to achieve stability by arranging an infinite return loss between the two directions of transmission, through the utilisation of switching arrangements so that amplified speech signals can be transmitted only in one direction at a time. The effective utilisation of such switching arrangements depends, however, upon the very rapid detection of the direction of transmission of a speech signal requiring amplification, and a correspondingly rapid switching of the amplifying system. Due to the recent advances in the technology of electronic gating, the rapid switching of the appropriate amplifier circuits presents little problem. The rapid detection of the direction of transmission of speech signals, however, poses more of a problem, and it has proved extremely difficult to provide an arrangement for reliably detecting the direction of speech transmission without at the same time increasing the time required for such directional detection to the extent that the intelligibility of transmitted speech is reduced by undesirable clipping of the beginnings of speech signals. It has proved difficult to detect the presence of low level signals from the distant end of the line whilst relatively larger signals are being applied to the line at the near end so that the distant end is able to interrupt and be heard.